Aldehydes, particularly linear paraffinic aldehydes, are extremely useful as intermediates in organic synthesis because of their terminal carbonyl group which is among the most active groupings in organic compounds. For instance, they are easily reduced and oxidized and take part in a number of addition reactions. More specifically, paraffinic aldehydes are readily catalytically reduced to the primary alcohols, and oxidized to the corresponding carboxylic acids. They also undergo addition and/or condensation reactions with hydrogen cyanide, alcohols, nitroparaffins as well as condensations with themselves and other carbonyl-containing compounds. Further, these aldehydes condense with ammonia and its derivatives including primary amines. The latter condensation products (which are commonly known as Schiff's bases) lend themselves to applications as surfactants or detergents when solubilized by processes such as sulfation or oxyalkylation.
Generally, aldehydes as a class are produced commercially by the catalytic addition of carbon monoxide and hydrogen to olefins in an outgrowth of the well known Fischer-Tropsch process. This procedure is known as the "oxo" process, or more accurately as hydroformylation. The generic reaction is set forth below for an .alpha.-olefin: ##STR1##
After an extensive research program the applicants have developed catalysts composed of ligand stabilized platinum(II) dihalide complexes with Group IVA metal halides that have several advantages over the known prior art. They include:
1. These catalysts permit successful operation of the hydroformylation process under relatively mild reaction parameters of temperature and pressure.
2. With these catalysts high olefin to catalyst ratios can be used without adversely affecting the advantages of the process.
3. These catalysts afford high yields of aldehydes, and selectivity to the more desirable straight chain aldehyde is high when .alpha.-olefins are hydroformylated.
4. Ordinary commercially available equipment may be used for the hydroformylation, and the use of relatively toxic cobalt or nickel carbonyls is avoided.
In view of this unusual combination of advantages, the inventive process represents an improvement in substance in view of the art.
In the broadest contemplated practice of this invention, aldehydes are produced in a catalytically directed addition of hydrogen and carbon monoxide to olefins by contacting at least a catalytic quantity of a ligand stabilized platinum(II) dihalide complex and a Group IVB metal halide catalyst at superatmospheric conditions of pressure, with said hydrogen, carbon monoxide and olefin until the desired formation of said aldehydes takes place.
In a preferred specific embodiment of the abovedescribed process essentially linear alkyl aldehyde products containing from 3 to 31 carbon atoms are prepared by the catalytic addition of hydrogen and carbon monoxide to alpha olefins containing 2 to 30 carbon atoms by the process steps comprising:
a. admixing each mole of said alpha-olefin to be hydroformylated in a deoxygenated reaction media with from 0.001 to 0.1 moles of a ligand stabilized platinum(II) dihalide complex and from 0.001 to 1.0 moles of a group IVA metal halide, said mole ratio of Group IVA metal halide: ligand stabilized platinum(II) dihalide complex ranging from 1/1 to 10/1,
b. pressurizing said reaction mixture to at least 100 psig with at least sufficient carbon monoxide and hydrogen to satisfy the stoichiometry of the hydroformylation reaction referred to supra, said mole ratio of H.sub.2 :CO ranging from 30:1 to 1:30 moles of hydrogen for each mole of carbon monoxide;
c. heating said pressurized reaction mixture to temperatures between 25.degree. to 125.degree.C, until substantial formation of the predominantly linear alkyl aldehyde product is formed, and
d. isolating said aldehyde products contained therein.
In still a further, preferred specific embodiment of the instant hydroformylation process, essentially linear alkyl aldehyde products containing from 3 to 31 carbon atoms are prepared from the catalytic addition of hydrogen and carbon monoxide to alpha-olefins containing 2 to 30 carbon atoms by the process steps comprising:
a. admixing under a deoxygenating reaction environment each mole of said alpha-olefin to be hydroformylated with a catalyst consisting of from 0.002 to 0.01 moles of a ligand stabilized platinum(II) dihalide complex and from 0.004 to 0.08 moles of a Group IVA metal halide, said mole ratio of Group IVA metal halide:ligand stabilized platinum(II) dihalide complex ranging from 2/1 to 8/1,
b. pressurizing said reaction mixture to superatmospheric pressures ranging from 500 to 1500 psig with at least sufficient carbon monoxide to satisfy the stoichiometry of said hydroformylation reaction, and excess hydrogen over what is required to satisfy the stoichiometry of said hydroformylation reaction, said mole ratio of H.sub.2 :CO ranging from 2/1 to 1/2 moles of hydrogen for each mole of carbon monoxide;
c. heating said pressurized reaction mixture to temperatures ranging between 50.degree. and 100.degree.C for a period of 1 to 30 hours to form the predominantly linear alkyl aldehyde product, and
d. isolating said product contained therein.
In order to further aid in the understanding of this invention, the following additional disclosure is submitted:
A. PROCESS SEQUENCE AND VARIATIONS
In general, the components of the hydroformylation reaction mixture, including optional inert solvent, olefin and catalyst may be added in any sequence as long as good agitation is employed to provide a good dispersion or a homogeneous reaction mixture. For example, the following represent some variations insofar as the addition of catalyst components, inert solvents and olefin addition that may be made without departing from the inventive process. These modifications include:
1. The catalyst may be preformed and added preformed to the reaction solvent prior to the addition of the olefin and other inert solvent components.
2. Preferably, to minimize stability problems with the catalyst, the catalyst is best formed in situ usually by mixing the deoxygenated inert solvent and neat olefin, followed by the addition of the excess metal halide of Group IVA, and finally by the addition of the ligand stabilized platinum(II) complex to form the reaction mixture.
3. After using either variation 1 or 2, the deoxygenated catalyst containing reaction mixture is pressurized with CO and hydrogen and heated until the aldehyde product is formed.
4. An especially preferred modification, which minimizes both the induction period and the isomerization of the olefin, is the following: the catalyst is formed in a deoxygenated solvent; the catalyst solution is pressurized with carbon monoxide and hydrogen and heated to the desired reaction temperature; olefin is then added neat or dissolved in a suitable solvent. The reaction mixture is agitated under CO and H.sub.2 at the desired reaction temperature until the aldehyde product is formed.
B. LIGAND STABILIZED PLATINUM(II)) TYPE - GROUP IVB METAL HALIDE CATALYST COMPLEX
The ligand-stabilized, platinum(II) type halide Group IVB metal halide complexes are known in the literature and methods for their preparation have been described.* One convenient mode of preparation in situ is to mix a solution of platinum(II) halide complex such as PtCl.sub.2 [P(C.sub.6 H.sub.5).sub.3]2, with a large molar excess of Group IVA metal halide, preferentially SnCl.sub.2. While no structural configuration is advocated, nor is the success of the catalyst postulated upon a given structure, it is assumed that such a typical ligand-stabilized platinum(II) typestannous chloride complex can be represented as: ##STR2## wherein Ph is the symbol for the phenyl radical (C.sub.6 H.sub.5). FNT *For example: R. D. Cramer et al. J. A. Chem. Soc., 85, 1691(1963)
The ligand stabilized platinum(II) halide catalyst is only effective in the presence of a Group IVA metal halide as is shown in Table I. Illustrative of the Group IVA metal halides, which can be utilized with the ligand stabilized platinum(II) halide complexes to form active hydroformylation catalysts are: tin(II) chloride, tin(II) bromide, tin(II) iodide, tin(IV) chloride, germanium(II) chloride. Tables I and II show evidence of the suitability of these Groups IVA metal halides.
The platinum(II) halide complex, which is utilized in the presence of a Group IVA metal halide, should contain additional ligands with donor atoms from Groups VA, VIA and VIIA of the "Periodic Chart of Elements" (taken from the text "Advanced Inorganic Ghemistry" by F. A. Cotton and G. Wilkinson, 2nd Edition, John Wiley and Sons, New York, 1966), and have the general formula: EQU Ptx.sub.2 (LIGAND).sub.m
wherein x is a halogen, and m is an integer 2 or 1 depending upon whether the said ligand is monodentate or bidentate.
One class of ligands containing Group VA donor atoms, preferably trivalent phosphorus or arsenic, may be defined by the general formula: EQU (R.sub.c A).sub.a -- B -- R.sub.b
wherein B represents the element from Group VA, preferably phosphorous or arsenic, R represents hydrogen atoms, aryl, alkyl, or aralkyl groups, which may contain less than 20 carbon atoms and need not be the same, A may represent oxygen, nitrogen or sulfur, or mixtures thereof, a has a value of 0 to 3, b has a value 3-a and c is equal to 1 or 2. It is also suitable for the organic radical R to contain functional groups, or to satisfy more than one of the valences of the Group VA atom, thereby forming a heterocyclic compound with the Group VA atom,
Another type of suitable ligand, containing Group VA donor atoms, is one which is comprised of two such Group VA atoms linked by organic radicals. This type of compound is called a bidentate ligand.
Another suitable class of Group VA ligands may be characterized by the formula: EQU (X).sub.a -B-(R).sub.b
wherein X may be an atom from Group VIIA, preferably chlorine and bromine, B represents a Group VA donor atom, preferably phosphorus and arsenic, R is an alkyl, aryl or aralkyl group which may contain less than 20 carbon atoms, and the sum of the integers a plus b is 3.
Another suitable class of ligands containing Group VA donor atoms consists of certain types of heteroaromatic ligands which may function as .pi.-acceptor ligands.* FNT *For a description of .pi.-acceptor ligands see Advanced Inorganic Chemistry by F. A. Cotton & G. Wilkinson, 2nd Ed. Chap. 27
Illustrative of suitable Group VA ligands which may be used with platinum(II) halides to form active hydroformylation catalysts in the presence of suitable Group IVA metal halides are:
__________________________________________________________________________ P(C.sub.6 H.sub.5).sub.3, P(n-C.sub. 4 H.sub.9).sub.3, P(p-CH.sub. 3.C.sub.6 H.sub.4).sub.3, P(CH.sub.3).sub.2 (C.sub.6 H.sub.5), As(C.sub.6 H.sub.5).sub.3, As(n-C.sub. 4 H.sub.9).sub.3, Sb(C.sub.6 H.sub.5).sub.3, Sb(n-C.sub. 4 H.sub.9).sub.3, Bi(C.sub.6 H.sub.5).sub.3, Bi(n-C.sub. 4 H.sub.9).sub.3, P(OC.sub.6 H.sub.5).sub.3, P(C.sub.6 H.sub.11).sub.3, (C.sub.6 H.sub.5).sub.2 P--CH.sub.2 --CH.sub.2 --P--(C.sub.6 H.sub.5).sub. 2, (C.sub.6 H.sub.5).sub.2 As--CH.sub.2 --CH.sub.2 As(C.sub. 6 H.sub.5).sub.2, P(Cl)(C.sub.6 H.sub.5).sub.2, P(Br)(C.sub.6 H.sub.5).sub.2, As(Cl)(C.sub.6 H.sub.5).sub.2, P(CH.sub.3)(C.sub.6 H.sub.5).sub.2, As(Br)(C.sub.6 H.sub.5).sub.2, 1,10-phenantholine, 2,2' dipyridyl, etc. __________________________________________________________________________
Suitable ligands having Group VI donor atoms include those having the general formula: EQU B - R.sub.b
where B represents the elements oxygen, sulfur, selenium, tellurium and polonium as donor atoms, R is selected from the group including alkyl, aryl, substituted aryl or alkyl groups or mixtures thereof, and b has a value of 2. These ligands should also be capable of functioning as .pi.-acceptor ligands. Examples of suitable Group VIB ligands are:
______________________________________ S(C.sub.6 H.sub.5).sub.2, Se(C.sub.6 H.sub.5).sub.2 ______________________________________
Ligands which are suitable in Group VIIA are fluorine, chlorine, bromine and iodine.
Table III and IV show evidence for the suitability of the above named ligands.
Illustrative of the many ligand stabilized platinum(II)-Group IVA metal halide complexes which can be used in the inventive hydroformylation as the catalyst system are:
__________________________________________________________________________ PtCl.sub.2 [As(C.sub.6 H.sub.5).sub.3 ].sub.2 --SnCl.sub.2, PtCl.sub.2 [Sb(C.sub.6 H.sub.5).sub.3 ].sub.2 --SnCl.sub.2, PtCl[Bi(C.sub.6 H.sub.5).sub.3 ].sub.2 --SnCl.sub.2, PtCl.sub.2 [P(C.sub.6 H.sub.5).sub.3 ].sub.2 --SnCl.su b.2, PtCl.sub.2 [P(C.sub.2 H.sub.5).sub.2 (C.sub.6 H.sub.5)]--SnCl.sub.2, PtCl.sub.2 [As(n-C.sub. 4 H.sub.9).sub.3 ].sub.2 --SnCl.sub.2, PtCl.sub.2 [(C.sub.6 H.sub.5).sub.2 P(CH.sub.2).sub.2 P(C.sub.6 H.sub.5).s ub.2 ]--SnCl.sub.2, PtCl.sub.2 [(C.sub.6 H.sub.5).sub.2 -- AsCH.sub.2 CH.sub.2 As(C.sub.6 H.sub.5).sub.2 ]--SnCl.sub.2, PtCl.sub.2 (1,10-Phenanthroline)--SnCl.sub.2 PtCl.sub.2 [P(n-C.sub. 4 H.sub.9).sub.3 ].sub.2 --SnCl.sub.2, PtCl.sub.2 [As(CH.sub.3).sub.2 C.sub.6 H.sub.5 ].sub.2 --SnCl.sub.2 PtCl.sub.2 [P(p-CH.sub. 3 --C.sub.6 H.sub. 4).sub.3 ].sub.2 --SnCl.sub.2, PtCl.sub.2 [2,2-dipyridyl]--SnCl.sub.2, PtCl.sub.2 (S(C.sub.6 H.sub.5).sub.2 ].sub.2 --SnCl.sub.2, PtCl.sub.2 [P(OC.sub.6 H.sub.5).sub.3 ].sub.2 --SnCl.sub.2, PtCl.sub.2 [P(Cl)(C.sub.6 H.sub.5).sub.2 ].sub.2 --SnCl.sub.2, __________________________________________________________________________
as well as the corresponding stannous bromides, stannous iodides, and stannic chlorides, bromides, and iodides and germanium(II) halide complexes. Tables I-IV show evidence for the suitability of the above ligand stabilized platinum(II)-Group IVA metal halide complexes as hydroformylation catalysts.
C. TEMPERATURE REQUIRED FOR HYDROFORMYLATION
The temperature range which can be employed for hydroformylation is a variable which is dependent upon experimental factors including the olefin employed, the total pressure, the mole ratio of hydrogen and carbon monoxide used, the concentrations of reactants and catalyst, and particularly the choice of platinum catalyst among other things. Again using 1-heptene as a typical alpha-olefin and PtCl.sub.2 P(C.sub.6 H.sub.5).sub.3 -SnCl.sub.2 as a representative catalyst, an operable temperature range is from about 25.degree. to 125.degree.C when superatmospheric pressures of greater than 100 psig are employed. A narrower range of 50.degree.C to 100.degree.C represents the preferred temperature range when the aforementioned olefin is hydroformylated at 500-1500 psig using the catalyst system described supra. Table V is evidentiary of how this narrower range is derived.
D. PRESSURES REQUIRED FOR HYDROFORMYLATION
The pressure range which can be employed for hydroformylation is a variable which is also dependent on the factors mentioned above. Using PtCl.sub.2 [P(C.sub.6 H.sub.5).sub.3]2 -SnCl.sub.2 as a representative catalyst, and 1-heptene as the olefin, an operable pressure range is from 100 to 3000 psig, with a mole ratio of H.sub.2 :CO being 1:1, when a temperature range of from about 25.degree. to 125.degree.C is employed. A narrower range of from 500 to 1500 psig represents the preferred pressure range when the narrower temperature range of 50.degree.C to 100.degree.C is employed. Table V provides supporting data of how this narrower range is derived.
E. HYDROGEN TO CARBON MONOXIDE RATIO
The H.sub.2 /CO mole ratio may be varied over a range of from 30/1 to 1/30 when suitable temperatures and total pressures are employed. A preferred narrower range is from 2/1 to 1/2 of hydrogen/carbon monoxide. Table VI gives data on the effect of H.sub.2 /CO ratio on yields, selectivity, and reaction times.
F. REACTION TIMES REQUIRED
As previously indicated in the analogous discussion on temperatures and pressures required in the reaction, experimental variables are important in arriving at reaction times, Generally, substantial conversions (80% or higher) of the olefin to the linear paraffinic aldehydes can almost always be accomplished within 10 hours, with 2 to 4 hours representing the more usual reaction time interval.
G. RATIO OF STANNOUS HALIDE TO LIGAND STABILIZED PLATINUM(II) TYPE CATALYST
While the molar ratio of stannous chloride to the ligand stabilized platinum(II) type halide is not critical, the experimental work performed indicates that at least 1 mole of stannous chloride for each mole of platinum(II) type chloride complex is required for reproducibility and good selectivity. Preferably a ratio of from 2 to 8 moles of stannous chloride for each mole of platinum(II) complex has been extablished to give the optimum amount of lenear paraffinic aldehyde at greatly increased rates of hydroformylation. This preferred ratio is based upon the hydroformylation of 1-heptene. Table VII documents this work.
H. RATIO OF LIGAND STABILIZED PLATINUM(II) TYPE HALIDE-CATALYST COMPLEX TO OLEFIN SUBSTRATE
Experimental work indicates that a molar ratio of up to 500 moles to 1000 moles of alpha olefin per mole of platinum(II) type catalyst complex can be employed in most instances where alpha-olefins (as typified by 1-heptene) are used as the substrate. This minimal ratio of 0.001 moles of catalyst per mole of olefin is herein referred to as a "catalytic ratio" or "catalytic amount". Much lower ratios (i.e. 25 moles of olefin substrate per mole of platinum catalyst complex) are not harmful but are economically unattractive For this reason the favored mole ratio range arrived at in Table VII ranges from 100 to 500 moles of alpha-olefin per mole of platinum catalyst complex. Preferably the molar ratio ranges from 200 to 400 moles of olefin per mole of platinum(II) catalyst complex.
I. INERT SOLVENTS
The novel hydroformylation is run most conveniently in the presence of an inert diluent. A variety of solvents can be used including ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, acetophenone, and cyclohexanone, aromatics such as benzene, toluene and xylenes, halogenated aromatics including ortho-dichlorobenzene, ethers such as tetrahydrofuran, dimethoxyethane and dioxane, halogenated paraffins including methylene chloride, paraffins such as isooctane, and other solvents such as acetonitrile. As the data of Table VIII indicate, the preferred solvents are polar ketones such as acetone, methyl ethyl ketone, diethyl ketone, methyl propyl ketone, methyl isobutyl ketone, and acetophenone.
J. OLEFINS AS SUBSTRATES
Olefins ranging in carbon content from 2 up to 30 carbon atoms can be employed as substrates for the hydroformylation reactions. Illustrative terminal (.alpha.-) olefin substrates include 1-propene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene as well as their higher homologues such as 1-heptadecene, 1-octadecene, 1-eicosene, 1-tricosene, 1-pentacosene. Illustrative branched chain .alpha.-olefin substrates include isobutylene, 2-methyl-1-pentene and 3-methyl-1-pentene. Illustrative internal and cyclic olefins include 2-butene, 2-pentene, 2-heptene, and cyclohexene, etc. These olefin substrates may be utilized in conjunction with one or more inert background solvents such as those mentioned above. The olefins can be in the form of single, discrete compounds or in the form of mixtures of olefins with or without large quantities of saturated hydrocarbon. In the latter case these comprise mixtures of from 2 to 30 carbon atoms. Table IX shows data for the hydroformylation of various olefins.
K. BY-PRODUCTS
As far as can be determined, without limiting the invention thereby, hydroformylation of olefins, catalyzed by the ligand-stabilized platinum(II)-Group IVA metal halide complexes, leads to the formation of only three minor classes of by-products. These are isomerized olefins, hydrogenated olefins and high boiling products, assumed to be condensation type products, which do not readily elute from our gas chromatography column.
The by-products may be separated from the linear paraffinic aldehydes by the usual chemical or physical techniques, such as distillation, solvent extraction, chromatography etc.
L. IDENTIFICATION PROCEDURES are by one of more of the following analytical procedures -- gas chromatography (g.c) infrared, elemental analysis and nuclear magnetic resonance. Unless otherwise specified all percentages are by mole rather than weight or volume, and all temperatures are in centigrade rather than fahrenheit.
M. CONVERSION as defined herein represents the extent of conversion of the reacting olefin to other products. Conversion is expressed as a percentile and is calculated by dividing the amount of olefin consumed during hydroformylation by the amount of olefin originally charged and multiplying the quotient by 100.
N. YIELD as defined herein, represents the efficiency in catalyzing the desired hydroformylation reaction relative to other undesired reactions. In this instance hydroformylation to paraffinic aldehyde is the desired conversion. Yield is expressed as a percentile, and is calculated by determining the amount of paraffinic aldehyde product formed, divided by the amount of olefin charged and multiplying the quotient obtained by 100.
O. SELECTIVITY as defined herein is the efficiency in catalyzing a desired hydroformylation reaction relative to other undesired reactions. When .alpha.-olefins are to be hydroformylated, hydroformylation to the linear paraffinic aldehyde is the desired conversion. Selectivity is expressed as a percentile, and is calculated by determining the amount of linear aldehyde product formed, divided by the total amount of aldehyde products formed and multiplying the quotient obtained by 100.